A head up display (HUD) of an automobile is adopted to ensure the security and stability of driving by a driver, such that the driver can see relevant information without lowering his/her head, and can pay more attention to the road condition. Thus, the visual fatigue of the driver due to frequently switching between viewpoints can be mitigated. A conventional HUD displays information mainly by projecting the information onto a front windshield of the HUD.
Since the front windshield has a certain thickness, for example, of 5 mm to 8 mm, the light is reflected at both an inner surface and an outer surface of the front windshield, respectively. In addition, since the front windshield has a certain curvature, ghosting will occur when the light reflected at the inner surface of the front windshield and the light reflected at the outer surface of the front windshield enter into the eyes of the driver. The ghosting will result in an error of recognition by the eyes of the driver, and will distract the driver from driving. Thus, at the present, how to eliminate the ghosting in the automobile-mounted HUD is a technical problem to be solved urgently.
At present, there exist two methods commonly used for eliminating the ghosting. In one method, the HUD includes a flat glass screen. However, the flat glass screen occupies certain space on the central console which has a limited size, thus the flat glass screen included in the HUD may easily block a portion of the windshield. In the other method, a polarizer film is provided in the front windshield to prevent the light reflected at the outer surface of the front windshield from emitting from the inner surface of the front windshield by using polarization of the light, such that the ghosting is eliminated. Both of these two methods cause a dark region having a certain area to appear in a portion of the front windshield which is in front of the driver, which reduces the security of driving by the driver.